1. Field of the Invention
This invention relates to a pacing lead with sensor mounted therein for measuring the occurrence of a phenomenon in a living organism, and more particularly, to a pacing lead having a piezoelectric sensor, the pacing lead being implanted in a living organism whereby the phenomenon acting on the sensor will generate an electric waveform indicative of the phenomenon. The phenomenon sensed is typically contractions of the heart.
2. Description of the Prior Art
Heretofore, various sensors have been developed for sensing phenomena occurring in living organisms, and particularly, the human body and heart. For example, cardiac sensors are disclosed in U.S. Pat. Nos. 2,634,721; 3,038,465; 3,410,441; 3,811,427 and 3,831,588. These sensors have utilized various complicated constructions, such as strain gauges in U.S. Pat. Nos. 2,976,865 and 4,003,370, field effect transistors in U.S. Pat. No. 3,946,724, PN type transducers in U.S. Pat. No., 3,710,781, and signal generating semiconductor devices in U.S. Pat. No. 3,811,427.
Further, it has been experimentally suggested to use piezoelectric sensors for measuring heart beats and blood flow by wrapping a band of piezoelectric material around a patient's chest or leg, including those of the ferroelectric polymer and polyvinylidene fluoride (PVF.sub.2) types. For example, see "Ferroelectric Polymers and their Application" by Michael A. Marcus, appearing in Ferroelectrics: 40, 1982, and "Piezoelectric High Polymer Foils as Physiological Mechanic-Electric Energy Converters" by E. Hausler, H. Lang and F. J. Schreiner, appearing in IEEE 1980 Bio Medical Group Annual Conference, Frontiers of Engineering in Health Care.
Further, it is known to implant a piezoelectric device in a living organism for other purposes, such as to: power a cardiac or other pacer as suggested in U.S. Pat. No. 3,659,615, and control or vary the pacing rate with the implantee's own physical activity as disclosed in U.S. Pat. No. 4,140,132.
It has also been known that under controlled clinical conditions one can, by placing a microphone on the chest of a person, measure the vibrations of the heart and obtain graphs of waveforms showing, at a minimum, the opening and closing of the heart valves. See, for example, "The Analysis and Interpretation of the Vibrations of the Heart, as a Diagnostic Tool and Physiological Monitor" by C. M. Agress, M. D. and L. G. Fields appearing in IRE Transactions on Biomedical Electronics, July 1961.
As will be described in greater detail hereinafter, it has been found from studies on dogs using a pacing lead having a piezoelectric sensor mounted in the distal end portion thereof in accordance with the teachings of the present invention, that graphs of waveforms can be obtained clearly showing the opening and closing of the heart valves. This can be significant since from measurements of opening and closing of the heart valves, one can determine stroke volume and then by multiplying stroke volume by heart rate, one can determine cardiac output.
Also as will be described in greater detail hereinafter, the present invention provides a method for controlling pacing of a heart relative to the changes in stroke volume using the pacing lead having a lead body and a pressure sensor mounted in the lead body near the end of the pacing lead. According to this method, openings and closings of a tricuspid valve in a heart are sensed by the sensor and such sensings are used to determine stroke volume.
Heretofore it has been proposed in Mirowski et al, U.S. Pat. No. 3,614,954 to mount a pressure sensing bulb on the outside of a pacing lead for the purpose of sensing pressure. These sensing are used to determine malfunctions of the heart so that the heart can be automatically defibrillated by sending electrical pulses to electrodes on the pacing lead from an electronic standby defibrillator electrically coupled to the pressure sensing bulb.
In the Denniston, III U.S. Pat. No. 3,815,611 an apparatus using a piezoelectric sensor is disclosed for sensing or detecting contractions of the muscles of living animals.
In the Zacouto U.S. Pat. No. 4,052,991 there is disclosed a method of stimulating a heat in response to pressure sensings sensed by a pressure detector mounted in the intraventicular septum of the heart, as shown in FIG. 19 of this patent.
In the Seo U.S. Pat. No. 4,191,193 there is disclosed a catheter head-type transducer for measuring pressure in a vessel of a body.
In the Anderson et al. U.S. Pat. No. 4,428,378 the disclosure of which is incorporated herein by reference, a rate adaptive pacer is disclosed which includes an activity sensor mounted within the pacer for detecting the general activity level of a patient and for then altering the escape interval of the pacer between a preset minimum and maximum in response to the detected activity level of the patient. The pacer includes signal processing circuitry which utilizes the sensed activity for controlling the rate of pacing.
In the Anderson et al. U.S. Pat. No. 4,485,813 there is disclosed an implantable dynamic pressure transducer system for detecting pressure and other force parameters for use with a pacemaker or other implanted cardiac monitoring and/or treatment device.
Finally, in the Olson U.S. Pat. No. 4,535,774 there is disclosed a stroke volume controlled pacer which employs a pacing lead having electrodes thereon positioned within a heart chamber for sensing changes in impedance in the heart chamber. Then, the changes in impedance in the heart chamber are used to infer stroke volume. This patent also suggests that stroke volume may be inferred by a variety of measurements taken in the right or left heart and including pressure-time histories of arterial blood flow, as well as direct flow measurements in the major blood vessels of the heart.
As will be described in greater detail hereinafter, the method of the present invention does not utilize pressure-time histories of arterial blood flow, direct flow measurements in major blood vessels of the heart or changes in impedance within a heart chamber. Instead, the method of the present invention utilizes sensings of the opening and closing of the tricuspid valve for determining ejection time and then from determinations of ejection time determining stroke volume and changes in stroke volume. The changes in stroke volume are utilized for controlling the pacing of a heart.